Asymmetric Contraction Research Articles

Average Time between Bursts in a Favorable pressure Gradient.

Effects of a favorable pressure gradient on the average time between bursts were studied by two different methods : the modified U-level method, and a proposed detection scheme that applies the U-level method to ejections and sweeps. Experiments were carried out in a boundary layer along a flat wall of two-dimensional asymmetric contraction. The results of experiments show that the average time between bursts scaled with inner variables increases with a decrement of the pressure gradient parameter Δp, and the ratio of the Eulerian micro-time scale to the average time between bursts gives a constant value of 0.1 at Y+=15. The proposed method also indicates that bursts still remain throughout the reverse transition process from a turbulent boundary layer to a laminar one.

Developmental and corrective biomechanics for scoliosis

The developmental mechanism for scoliosis and its surgical correction are studied by modeling the spinal column as a curved nonlinear (large-deformation-sustaining) beam column to which are applied (a) muscle forces to simulate scoliosis development due to asymmetrical bilateral muscle contractions and (b) corrective forces to simulate the action of surgically implanted corrective systems. The two-dimensional model permits curvature in the frontal plane and can simulate and demonstrate the progression of a scoliotic curve from an initially straight configuration for various model parameter values. The calculation of the bonding moments is treated, and a simple algorithm for solving the model equations is presented. Results for an actual clinical case are given.

Immunocytochemical localization of cholinergic terminals in the region of the nucleus basalis magnocellularis of the rat: A correlated light and electron microscopic study

The cholinergic circuitry in the nucleus basalis magnocellularis of the rat was investigated in a correlated light and electron microscopic study by using monoclonal antibodies against the acetylcholine-synthesizing enzyme, choline acetyltransferase, following the unlabelled antibody peroxidase-antiperoxidase immunocytochemical procedure. After the immunocytochemical approach, large cholinergic cells and a few immunoreactive fibres exhibiting a varicose appearance, were detected by light microscopy in portions of the nucleus basalis magnocellularis located within the anatomical limits of the globus pallidus, mostly in its ventromedial part. Cholinergic neurons and fibre-like structures were also found within the substantia innominata on the edge of globus pallidus.The same material studied by light microscopy was analysed with the electron microscope. At the ultrastructural level, the immunopositive neurons showed the same cytological characteristics and pattern of synaptic input as cholinergic basal forebrain cells. Additionally, scarce immunoreactive preterminal axons and terminal boutons were detected in the region. The immunoreactive terminals were scattered or formed occasional clusters and appeared as heavily immunostained vesicle-filled boutons making exclusively axodendritic synaptic contacts principally with immunonegative distal dendrites. Both symmetric and asymmetric synaptic contacts established between these structures were detected, although the symmetric contacts were the more numerous. The surface of postsynaptic immunonegative dendrites in asymmetric synaptic contact with immunoreactive terminals was generally covered by terminals that lacked detectable immunoreactivity. In contrast, those in symmetric synaptic contact with labelled terminals showed much sparser input from immunonegative terminals, suggesting that they may belong to interneurons. Very rarely, cholinergic terminals were detected in asymmetric synaptic contact with dendrites which also contained positive immunoreaction product. Asymmetric contracts were frequently characterized by the presence of subjunctional dense bodies.The detection of cholinergic terminals in the region of the nucleus basalis magnocellularis of the rat indicates that this region not only contains cholinergic projecting neurons, but receives a cholinergic input itself. Results of this study provide evidence of the existence of a cholinergic transmission in the basal forebrain of the rat, and also that acetylcholine might play a role in the regulation of the extrinsic cortical cholinergic innervation. The possible sources of this innervation are discussed.

Flows Through Round Sudden Contractions

Measurements of the mean axial and radial components of velocity, the r.m.s. of the corresponding fluctuations and the wall static pressure are reported for flows through round sudden axi- and asymmetric contractions with an area ratio of 2.5 and were obtained at a Reynolds number of 40 000 based on the bulk velocity in the upstream pipe. In the axisymmetric case, the main changes in the approach velocity profiles occurred within a distance of one-half diameter upstream of the contraction, and the velocity profiles suggested that the flow separates at the entrance to the smaller diameter pipe. The wall static pressures revealed the presence of a vena-contracta downstream of the contraction plane. In the asymmetric case, the velocity profiles were very three-dimensional but regained symmetry by 9.5 diameters from the contraction plane.

Pupal ecdysis in flies: Mechanisms of evagination of the head and expansion of the thoracic appendages

The development of pupal thoracic structures from imaginal discs proceeds in three steps: (1) The discs evaginate (evert and unfold to produce the general shapes of the adult structures), (2) the evaginated discs are inflated with haemolymph, and, (3) the inflated structures expand to form their definitive pupal shapes (specific internal components will migrate into these structures and differentiate into adult organs). Evagination of the head and inflation of the appendages is attained by peristaltic abdominal muscular contractions during the ecdysial phase of pupation. Relatively low haemolymph pressure (3.8 Torr) is needed to accomplish this. Morphogenesis of pupal structures is completed during the prolonged period of vigorous muscular activity accompanying the expansion stage. The pressure in the haemocoel reaches a value greater than 15 Torr at this time, being produced by asymmetrical contractions of the abdominal muscles. Swaying lateral movements caused by these contractions seem to be indispensible for extrication of the larval tracheal lining from the spiracles.

Physiological studies of conducting systems in the colonial hydroid Hydractinia echinata 1. Polyp specialization.

AbstractElectrical activity generated by electrical stimuli has been recorded through suction electrodes placed on gastrozooid and dactylozooid polyps of the colonial hydroid, Hydractinia echinata Flemming. The polymorphism so characteristic of a Hydractinia colony extends to the physiological machinery controlling the behavior of the different polyp types. Contraction of gastrozooid polyps, where the muscle elements are uniformly distributed within the epidermis, is correlated to an electrical event termed the symmetrical contraction potential (SCP). The SCP is conducted about 4.4 cm/sec. Two kinds of electrical activity are correlated to distinct behavioral events of the specialized asymmetrically coiled dactylozooid polyps: (1) Dactylozooid coiling potentials (DCPs) are conducted at about 4.6 cm/sec and are correlated with contraction of a thin band of muscles on the concave side resulting in asymmetrical contraction and a marked coiling of the polyp. (2) Dactylozooid lashing potentials (DLPs) are conducted at about 9.1 cm/sec and have a threshold 50 per cent or more higher than DCPs. DLPs are correlated with contraction of well‐developed muscles on the convex side resulting in a rapid uncoiling or “lashing” of the dactylozooid polyp. Dactylozooid coiling is correlated to an incremental spread of conduction within the colony whereas lashing occurs during colony‐wide through‐conducted excitation. Very small electrical spikes (50–200 μV amplitude) have been recorded from both gastrozooids and dactylozooids. These tiny potentials (TPs) are conducted at 15–21 cm/sec, have a threshold below that of the DCPs and SCPs, and are of unknown behavioral significance. On the basis of the characteristics of the electrical events, the differences in threshold, conduction velocity, and related spread of excitation, it is proposed that these three potentials represent activity within separate conducting systems — an incrementing conducting system (ICS), a through conducting system (TS), and a tiny potential system (TPS). Physiological and microscopical evidence suggest a nerve net origin for the ICS, and epithelial conduction for the TS.

Astigmatism of the lens by asymmetric contraction of the ciliary muscle.

A solution of pilocarpine was applied with a cotton wool pledget to the surface of the bulbar conjunctiva. This resulted in astigmatism by asymmetric contraction of the ciliary muscle. This seems to confirm that the ciliary muscle belongs to the multiple unit class of smooth muscles.

Inviscid Shear Flow with Corner Eddies

Steady rotational flow of an inviscid fluid in a two-dimensional channel with symmetrical, asymmetrical abrupt contractions and also flow in a circular channel with a symmetric abrupt contraction is treated. The velocity distribution far upstream is approximated either by a cosine or a sine curve in a two-dimensional channel and by a parabolic curve for the axisymmetric case. The linear differential equations are solved exactly which give the streamline pattern at the region immediately preceding the contraction. Flow through small discharge openings is arrived at by the use of a line or point sink.

Structure and function of the locomotory system ofPolyorchis montereyensis (Cnidaria, Hydrozoa)

1. The structure and function of the locomotory system of the anthomedusanPolyorchis montereyensis Skogsberg were studied in detail. Anatomical investigations were carried out primarily on fresh or formalin fixed specimens; histology was done on specimens fixed in Bouin's fluid. Functional analyses were based largely on photography and cinematography. 2. Swimming inP. montereyensis involves the alternating antagonistic action of the subumbrellar swimming muscles and the elastic mesoglea. 3. The swimming muscle consists of striated contractile elements arranged circularly in four discontinuous subumbrellar sheets and a sheet on the subumbrellar side of the velum. There is also a sheet of radially arranged fibers on the exumbrellar side of the velum. The four subumbrellar sheets are anchored to the bell along the perand interradii. 4. The mesogleal skeleton consists of five components: (a) the matrix of the bell mesoglea, (b) optically visible fibers that traverse the bell from gastrodermal lamella to exumbrella, (c) the basement membrane or supporting lamella, (d) a system of joints, and (e) the velar mesoglea. 5. The morphology, orientation, and distribution of the mesogleal fibers suggest that their major role is maintaining the radial integrity of the bell during deformation. The amount of stretch in a region of the bell wall during contraction is inversely proportional to the number of fibers per unit area there. In regions of the bell which are not deformed during contraction fibers are sparse or absent. 6. Mesogleal volume remains constant during swimming. Locally the mesoglea is subjected to forces of stretch and compression, but the critical element in narrowing the bell involves bending or folding the mesoglea around a series of structural joints. The fulcrum of these joints is anchored to the exumbrella by concentrations of mesogleal fibers. The joints consist of eight adradial regions of highly deformable mesoglea lacking visible fibers. The regions are triangular in cross section and are separated from the remainder of the mesoglea (98–99 % of the total) by the gastrodermal lamella. A circular apical joint is also present. 7. Sequential changes in shape and position of the bell relative to a fixed grid during contraction and recovery were measured in order to determine such parameters of swimming as rate of contraction, rate of expulsion of water, change in bell velocity during contraction and recovery, momentum, etc. 8. The function of the velum was determined by cinematographic analysis of swimming animals both before and after removal of the velum. In normal swimming the velum serves mainly to constrict the aperture of the bell, thus increasing the velocity of expelled water, and hence increasing the force driving the medusa foward. Medusae swam with a greatly decreased velocity after velum removal. 9. Turning is accomplished primarily by asymmetrical contraction of the exumbrellar velar radial muscles, whereby the velar aperture is displaced to one side, water is expelled obliquely, and the bell turns toward that same side. The ability to turn was lost after velum removal. 10. Studies of the relationship between individual size and the various parameters of swimming inP. montereyensis show that: (a) the duration of the contraction phase of the swimming beat is roughly proportional to the square root of the subumbrellar circumference (or bell height); (b) smaller individuals swim faster relative to their bell height than do larger ones; (c) the velum is relatively better developed in small animals and plays a proportionately more important role during swimming.

Two-Dimensional Flow with Corner Eddies

Analysis of flow in 2-dimensional channel with asymmetrical abrupt contraction; it is assumed that flow is steady and rotational and fluid inviscid; velocity distribution far upstream from contraction is approximated by sine curve; solution of governing differential system shows streamline pattern at region immediately preceding contraction.

The coordination of the uterus in labor

In this paper two cases of asymmetrical contractions of the uterus in labor are reported. These cases raised the question of the mechanism concerned. A review of the embryology, comparative anatomy, and physiology of the uterus shows that it has a bilateral origin and that the two halves except where fused act more or less independently. On fusion a correlating mechanism becomes manifest.A type of coordinated activity manifested by the postpartum uterus of the dog has been studied. An extrinsic and intrinsic mechanism has been discovered, one resident in the uterine wall and the other in the uterovaginal ganglia, the former being the most important; and it has been found that the dog's uterine motor mechanism in situ manifests the phenomena of refractory period and “summation.” On the basis of a functionally defective coordinating mechanism, the irregularity in the uterine motility, obliquity of the uterus, in the two cases observed, is explained and a basis for the explanation of other types of abnormal motor activity is offered.